Electric clock system



July s, 1941.

F. C, HOL-rz ELECTRIC CLOCK SYSTEM Filed July 2. 1938 Patented July 8,1941 ELECTRIC CLOCK SYSTEM Frederick C. Holtz, Springfield, lll..assignor to Sangamo Electric Company, Springfield, Ill., a corporationof Illinois Application July 2, 1938, Serial No. 217.298

(ci. sri- 24) 11 Claims.

My invention relates. generally, to time distributing systems and it hasparticular relation to electrically operated time distributing systemsin which a commercial alternating current source is employed.

It is now the generally accepted practice to operate electric clocksfrom a commercial alternating current source such as a sixty-cyclesource. Ordinarily the frequency of commercial alternating currentsources is accurately controlled so that, during normal operation, theclocks connected thereto provide an accurate indication of the time.Generally, there are two types of clocks that are employed for thispurpose.

One of these types is the self-starting clock. 'I'his clock is providedwith a synchronous electric motor that is automatically brought up tosynchronous speed as soon as it is energized.

The other type of clock is the non-self-starting clock. This clockrequires some means for` starting it in operation on its beingenergized.

This may take the form of an extended shaft which is manually rotate'dto bring the rotor up to the desired speed.

, As indicated, both of these types of clocks depend for their accuracyupon the accuracy of the control of the frequency of the commercialalternating current source. If this frequency varies above or below agiven frequency,v for example sixty cycles,l then the accuracy of theclocks varies accordingly.

Certain difficulties are encountered when the commercial alternatingcurrent source fails. In such case the clocks are immediatelydeenergized and, of course, they stop. When the service is restored, theself-starting clocks are placed automatically in operation but they areinaccurate in an amount corresponding to the period of serviceinterruption. In order to indicate that the power has failed and thatthe time indicated by the clock is not correct, certain types ofself-starting clocks are provided with indicators which are operated onfailure of the commercial alternating current source to show that theclock should be reset. The stoppage of the non-selfstarting clock, ofcourse, indicates that the service has failed and it is common practiceto reset them before manually restarting them.

It will be obvious that there are certain disadvantages inherent ineither of these types of clocks either because of variations in thefrequency of the commercial alternating current source or because offailures thereof for periods of sufiicient length to permit the clocksto stop.

The object of my invention, generally stated,

.is to provide an improved time distributing system which shall besimple, efficient, and accurate in operation and which may be readilyand economically installed.

An object of my invention is to derive a given frequency for an electricclock circuit from a commercial alternating current source regardless ofthe variations of the frequency of the cor'nmercial alternating currentsource.

Another object of my invention is to derive a given number ofalternations of current from a commercial alternating current source andapply them to an electric clock circuit Within a given period of timeregardless of variations of the frequency of the commercial alternatingcurrent source or even failure thereof.

A further object of my invention is to energize an electric clockcircuit from a commercial alternating current source and regulate thefrequency of the electric clock circuit'independently of the frequencyof the commercial alternating current source.

Still another object of my invention is to totalize the number ofalternations that would otherwise have been applied to an electric clockcircuit from a commercial alternating current source during periods offailure thereof and to apply a like number to the electric clock circuiton restoration of the commercial alternating current source in additionto the number normally applied to reset the electric clocks to the timeof a master clock.

According to my invention, I provide for energizing an electric clockcircuit to Which a plurality of electric clocks may be connected from acommercial alternating current source through a frequency converter. Ifthe frequency of the alternating current source is the same as theoperating frequency of the electric clock circuit, this frequency is feddirectly through the frequency converter. However, if the frequency ofthe commercial alternating current source is above or below the givenfrequency of the electric clock circuit, then the frequency converter isoperated in one direction or the other to decrease or increase thefrequency that is fed thereby from the commercial alternating currentsource to the electric clock circuit. The frequency converter operatesunder the control of a master clock. Means are provided, in the event offailure of the commercial alternating current source, for totalizing thenumber of alternations that wouldctherwise have been applied to theelectric clockcircuit during the period 'of failure and then applyingthem to the electric clock circuit on restoration ofthe commercialalternating current source in addition to the number that are normallyapplied thereby in order to reset the electricclocks to the time of themaster clock.

Other objects of my invention will, in part, be obvious and, in part,appear hereinafter.

My invention, accordingly, is disclosed in the embodiment thereof shownin the accompanying drawing, and it comprises the features ofconstruction, combination of elements and arrange- -ment of parts whichwill be exemplified in the construction hereinafter set forth, and thescope of the application of which will be indicated in the appendedclaims.

For a more complete understanding of the nature and scope of myinvention reference may be had to the following detailed descriptiontaken in connection with the accompanying drawing in which the singlefigure diagrammatically represents a concrete embodiment of myinvention.

Referring now particularly to the single figure in the drawing, it willbe observed that the reference character III designates, generally, acommercial alternating current source, such as a sixty-cycle sourcewhich is arranged to energize line conductors II. It will be understoodthat the source I I) and conductors II are merely illustrative of anysuitable alternating current source and distribution system providedwith the usual generators, transformers, and the like.

A special electric clock circuit, formed by the pair of conductors I2,is provided for energizing any desired number of electric clocks,' showngenerally at I3, and each having a field winding I4. The clocks I3 maybe of either of the two general types described hereinbefore, althoughthey are, preferably, of the self-starting type. Since the features ofconstruction of the clocks I3 are well known and form no part of thepresent invention, these clocks are illustrated diagrammatically onlyand the details of construction thereof will not be set forth herein.

The electric clock circuit I2 is arranged to be energized through afrequency converter, shown generally at I5, from the conductors II andcommercial alternating current source III. The frequency converter I5 isof conventional type. It comprises a construction that is similar tothat of a wound rotor polyphase induction motor having a distributedstator winding, illustrated at I 6, and a wound rotor with slip ringsillustrated at I1. For purposes of illustration a polyphase frequencyconverterv I5 is shown, but it will be understood that a single phasefrequency converter may be employed if desired. Since it is desirable toenergize the electric clock circuit I2 with single phase alternatingcurrent only, two of the slip rings of the rotor I1 are connected byconductors I8 across the electric clock circuit I2, as shown.

Now, as long as the rotor I1 of the frequency converter I5 remainsstationary, the frequency applied to the electric clock circuit I2 willbe that applied to the line conductors II by the commercial alternatingcurrent source II). When the rotor I1 is rotated by external means inthe direction in which the field of the stator I8 rotates, then thefrequency applied to the electric clock circuit I2 will be less than thefrequency of the commercial alternating current source IIi. In likemanner, when the rotor I1 is rotated by the external means in theopposite direction to that in which the field of the stator I8 revolves,the frequency that is applied to the electric clock circuit I2 isgreater than the frequency which is applied to the line conductors II bythe commercial alternating current source Il. By controlling the amountand direction of rotation of the rotor I1, it is possible to maintain agiven frequency on the electric clock circuit I2 regardless ofvariations in the frequency applied by the commercial alternatingcurrent source Il and to take care of failure of the same for shortperiods. The manner and means whereby this is accomplished will now beset forth.

With a view to driving the rotor I1 a reduction gearing mechanism, showngenerally at 28 is provided. It is provided with a worm wheel 2I that ismounted on a shaft 22 on which the rotor I1 is also mounted. A worm 23carried by a shaft 24 engages the teeth of the worm wheel 2 I, as shown.The rotor 25 of a reversible motor, shown generally at 25, is secured tothe shaft 24. I'he motor 26 is provided with field windings 21 and 28that may beenergized from a suitable source 29 of alternating currentfor operating the motor 25 in one direction or the other, depending uponwhether the field winding 21 or the field winding 28 is energized. Aswitch, shown generally at 30, is provided for selectively energizingthe field windings 21 and 28. It comprises a switch arm 32, which, asshown, is arranged to engage either stationary contact member 33,connected to the field winding 21, or stationary contact member 34,connected to the eld winding 28. The switch arm 82 is mounted forrotation with a shaft 35 that carries a gear wheel 36 meshing with aring gear wheel 31 of a differential gear mechanism, shown generally at38.

The differential gear mechanism 38 is typical of any suitabledifferential mechanism that may be employed for effecting the desiredmovement of the switch arm 32 in accordance with certain predeterminedconditions. It comprises a pair of planet wheels 33, suitably mounted onthe ring gear Wheel 31, and arranged to mesh with spur wheels 4U and 4I.

The spur wheel 40 is connected through a lost motion mechanism, showngenerally at 44, to a master clock, shown generally at 45. The masterclock 45 may be of any suitable type, such as a clock provided withpendulum 46, that may be used as a standard because of its accurate timekeeping qualities. It may be driven by any suitable manner such as by aspring or weight. as will be readily understood.

The master clock 45 is arranged to drive a shaft 41 on which is mounteda wheel or disc 48, forming a part of the lost-motion mechanism 44. Apin 48 projects axially from one side of the Wheel or disc 48 into thepath of another similar pin 5I'I that is Acarried by a wheel or disc 5Imounted on a shaft 52 for rotation therewith. A spiral spring 53 isprovided with one end fastened to the shaft 52 and the other endfastened to the pin 49 for biasing the pin 48 into engagement with thepin 50 during normal operating conditions.

The spur wheel 4I of the differential gear mechanism 38 is connectedthrough a lost-motion mechanism 54 to a synchronous motor, showngenerally at 55. The motor 55 may be of any suitable self-starting typeand it has a field winding 56 that is connected for energization acrossthe electric clock circuit I2, as shown. The motor 55 is also providedwith a rotor 51 that is mounted for rotation with a shaft 58.

The lost-motion mechanism 54 is similar in construction to that of thelost-motion mechanism 44, previously described. It comprises a wheel ordisc 53 that is mounted for rotation with the shaft 6I and that carriesa pin 60 pro- Jecting axially therefrom into the path of a, pin 6I thatis carried by a wheel or disc 62 fastened on a shaft 63 on which thespur wheel 4| is secured. A spiral spring 64, having one end connectedto the .pin III and the other end connected to the shaft I3 serves tobias the pins 60 and 6I into engagement under normal operatingconditions. q

In describing the functioning of my improved time distributing system,it will first be assumed that the frequency applied by the commercialalternating current source I through the frequency converter I6 to theelectric clock circuit I2 is exactly the frequency that is required tokeep the electric clocks I3 in synchronism with the master clock-46. Inother words, the time spur wheel 4I in the direction indicated by thearrow 63 thereon. Under the assumedmonditions the speed of rotation ofthe spur wheels 40 and 4I is the same and they rotate in oppositedirections. Therefore, the ring gear wheel 31 remains motionless andthere is no rotation of the gear wheel 36 and, consequently, no movementof the contact arm 32. It floats in some position between the stationarycontact members `33 and 34. Since neither of the field windings 21 and28 of the motor 26 is energized, its rotor 25 is stationary as islikewise the rotor I1 of the frequency converter I5.

Assuming now that the frequency of the commercial alternating currentsource Ill is increased, for example is increased to sixty-one orsixty-two cycles per second, then the frequency applied to the electricclock circuit I2 is above the given frequency and the electric clocks I3become fast. Likewise the rotor 51 of the synchronous motor 66 isrotated at a higher speed and, consequently, the spur wheel 4I rotatesin the direction indicated by the arrow 69 at a speed that is higherthan that of the spur wheel 40. As a result, the ring gear wheel 31 isrotated in such direction as to rotate the gear wheel 36 in thedirection indicated by the arrow 16. The contact arm 32 is then movedinto contact engagement with the stationary contact member 34 and thereversible motor 26 is energized. The rotor 25 is then caused to rotatethe rotor I1 of the frequency converter I in the direction in which therotating field of the stator I6 revolves to reduce the frequency that isapplied to the electric clock circuit I2 below the frequency that isapplied to the line conductors I I bythe commercial alternatlng currentsource I0. As soon as the frequency on the electric clock circuit I2 isreduced, the speed of the synchronous motor 55 is reduced and thecontact arm 32 is no longer held in contact engagement with thestationary contact member 34. If desired, centering springs 32' may beprovided for the contact arm 32 for the purpose of moving it out ofcontact engagement with either of the stationary contact members 33 or34 once the force urging it into contact engagement with either of themis removed. If the frequency of the commercial alternating currentsource I0 remains above the given frequency lntended to be applied tothe electric clock circuit I2, then the foregoing cycle oi' operationswill be repeated so that the total number of alternations applied to theelectric clock circuit I2 in any given period will be the sameregardlesslof the frequency of the commercial alternating current sourceIII.

If the frequency applied to the electric clock circuit I2 should remainabove the given frequency for a vconsiderable period of time, thecontact arm 32 would remain in engagement with the stationary contactmember 34. Ordinarily, the frequency converter I5 will be arranged toprovide a variation of ten percent, for example, above or below thefrequency applied thereto from the line conductors Il by the commercialalternating current source I Il. It may happen that the frequency of thecommercial alternating current source I0 will be above the frequency forwhich the frequency converter I5 can compensate. In such case, thecontact arm 32 remains in contact engagement with the stationary contactmember 34 and, since the gear wheel 36 is prevented from rotatingthereby, the ring gear wheel 31 remains stationary, The speed of thesynchronous motor then is such that the wheel or disc 59 directlyconnected thereto rotates at a higher speed than the wheel or disc 62 ispermitted to rotate because of the mechanical connection through thedifferential gear mechanism 38 to the master clock 45. The pin GIIy isthen moved away from the pin 6I and the spiral spring 64 is furthertensioned. The separation of the pins -and 6I is measure of thedeparture of the number of alternations applied to the electric clockcircuit I2 above the number that should have been applied in a givenperiod. Assuming that the frequency of the com-4 with respect to the pin6I will be restored to that shown in the drawing, at which time thecontact arm 32 will separate from the stationary contact member 34 andthe reversible motor 26 will be deenergized.

Assuming now that the frequency of the commercial alternating currentsource falls below the` given frequency intended to be applied to theelectric clock circuit I2, then the speed of the rotor 51 of thesynchronous motor 55 is reduced and there is a corresponding reductionin the speed of rotation of the spur wheel 4I as compared to the speedof rotation of the spur wheel 40. As a result, the ring gear wheel 31 isrotated in a direction opposite to that pre- 7@r viously described tocause the gear wheel 36 to rotate in a direction the reverse of thatpreviously described. The rotor I-1 of the frequency converter I5 isthen rotated in a direction opposite to the rotation of the field of thestator I6 and a frequency is applied t the electric clock circuit I2that is higher than the frequency which is applied to the conductors IIby the commercial alternating current source I0. This continues untilthe time indicated by the electric clock I3 corresponds to the time ofthe master clock 45. At this instant the spur Wheels 40 and 4I of thedifferential gear mechanism 3B are rotating in opposite directions atthe same speed and, therefore, the contact arm 32 is permitted to moveout of engagement with the stationary contact member 33.

It will now be obvious that the contact arm 32 will move between eitherextremes of its position into Contact engagement with either of thestationary contact members 33 or 34 depending upon whether the frequencyof the commercial alternating current source Il) is above or below thegiven frequency at which the electric clock circuit I2 is intended tooperate. The contact arm 32, as indicated hereinbefore, will floatbetween these two extreme positions when the frequency of the commercialalternating current source I0 corresponds to the desired frequency forenergization of the electric clock circuit I2.

The lost motion mechanism 44 functions in a manner similar to that of alost motion mechanism 54, previously described, when the frequency ofthe commercial alternating current source I0 remains for a considerableperiod below the given frequency of the electric clock circuit I2. Thelost motion mechanism 44 is of particular importance when the commercialalternating current source I0 fails completely for some interval, suchas for ten or fifteen minutes. In such case the electric clock circuitI2 is not energized and, of course, the electric clocks I3 are stopped,Likewise, the synchronous motor 55 is deenergized and no rotation of itsrotor 51 or of the spur wheel 4I driven thereby takes place. The gearwheel 36 is then rotated in a direction indicated by the arrow 1I, sincethe shaft 41 driven by the master clock 45 continues to revolve, and thecontact arm 32 engages the stationary contact member 33. Since thecommercial alterna-ting current source I0 has failed under the assumedconditions, operation of the reversible motor 26 to rotate the rotor I1of the frequency converter I is ineffective to restore the desiredfrequency to the electric clock circuit I2.

However, the shaft 41 driven by the master clock 45 continues to rotateand drives the wheel or disc 48 carried thereby in the directionindicated by the arrow 6E. Since the contact arm 32 is stopped incontact engagement with the stationary contact member 33, and the spurwheel 4I is motionless, no rotation of the spur wheel 40 or the wheel ordisc 5I is permitted. Consequently, the pin 49 carried by the wheel ordisc 48 moves out of engagement with the pin carried by the wheel ordisc 5I. The spiral spring 53 is tensioned.

Assuming now that the commercial alternating current source I0 isrestored before the pin 49 rotates through approximately 360 relative tothe pin 50, and that this frequency is that at which the electric clockcircuit I2 is intended to operate, then the contact arm 32 will remainin contact engagement with the stationary contact member 33 and thereversible motor 25 will drive the rotor I1 of the frequency converterI5 in the direction opposite to the rotation o1' the rotating eld of thestator I6 tc apply to the electric clock circuit I2 a frequency which ishigher than the normal frequency. The electric clocks I3 will then beoperated 'at a faster speed than the normal speed until the timeindicated thereby corresponds to that of the master clock 45. At thisinstant the pin 49 will have returned into engagement with the pin 50,as shown in the drawing, and the arm 32 will be permitted to move out ofcontact engagement with the stationary contact member 33. The systemwill then continue to operate under normal operating conditions, aspreviously described, until there is some change in the frequency of thecommercial alternating current source III.

It will now be obvious that I have provided a time distributing systemin which the electric circuit to which the electric clocks are adaptedto be connected will have a given number of alternations applied theretoin a given period as measured by the master clock from a commercialalternating current source regardless of variations in frequency 'ofthis source and even failure thereof. Of course, it will be understoodthat there are certain limits in this range of regulation but for allpractical purposes this statement of functioning of the system can beconsidered to correctly represent how it operates. Therefore, it isunnecessary to carefully note whether a clock connected to my improvedtime distributing system has its indicator operated to denote that theservice has failed, as in the case of certain self-starting clocks aspreviously described or to note that the clock of the non-selfstartingtype has stopped and should be restarted and reset, also as previouslydescribed. All of the clocks connected inv a time distributing system ofthe type herein described, are automatically kept in synchronism withthe master clock which can, of course, be easily regulated to keepaccurate time. Such a system is particularly advantageous when theclocks are located at places where it is inconvenient to reach them forresetting or restarting them.

It is likely that the commercial alternating current source I0 may failfor a. period that is longer than can be compensated for by any givencontrol mechanism, as described herein, then an auxiliary source ofalternating current can be provided which would be automaticallyconnected to the line conductors II a predetermined time after thecommercial alternating current source I0 failed. However, it isextremely unlikely that such an auxiliary power supply would be requiredin view of the rare occurrence of a. power failure for periods longerthan a few minutes.

Since certain further changes may be made `in the above construction anddifferent embodiments of the invention may be made without departingfrom the scope thereof, it is intended that all matter contained in theforegoing description or shown in the accompanying drawing shall beinterpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In a time distributing system, the combination with a commercialalternating current source of an electric clock circuit adapted to havea plurality of electric clocks connected thereto, means interconnectingsaid commercial alternating current source and said electric clockcircuit, master clock means, and means con- .trolled by said masterclock means for increasing and decreasing the frequency applied to saidelectric clock circuit as a function, respectively,

of its departure below and above a predetermined frequency independentlyof the frequency of said commercial alternating current source.

2. In a time distributing system, the combination with a commercialalternating current source of an electric clock circuit adapted to havea plurality of electric clocks connected thereto, means interconnectingsaid commercial alternating current source and said electric clockcircuit, master clock means, and means controlled by said master clockmeans and in accordance with the frequency of said electric clockcircuit for increasing and decreasing said frequency as a function,respectively, of its departure belowand above a given frequencyindependently of the frequency of said commercial alternating currentsource.

3. In a time distributing system, the combination with a commercialalternating current source of an electric clock circuit adapted to havea plurality of electric clocks connected thereto, frequency transfermeans interconnecting said commercial alternating current source andsaid electric clock circuit, master clock means, and differential meanscontrolled by said master clock'means and in accordance withvthefrequency of said electric clock circuit for regulating the operation ofsaid frequency transfer means in such manner as to apply a frequency tosaid electric clock circuit that is higher than the frequency of saidcommercial alternating current source in the event that the same islower than a given frequency and to apply a frequency to said electricclock circuit that is lower than the frequency of said commercialalternating current source in the event that the same is higher thansaid given frequency.

4. In a time distributing system, the combination with a commercial.,alternating current source of an electric clock circuit adapted to havea plurality of electric clocks connected thereto, a frequency converterinterconnecting said commercial alternating current source and saidelectric clock circuit, means for driving said frequency converter inone direction or the other to apply substantially a given frequency tosaid electric clock circuit substantially regardless of the frequency ofsaid commercial alternating current source, and means for controllingthe functioning of the driving means in accordance with the departure ofthe frequency applred to said electric clock circuit from said given"frequency. i

5. In a time distributing system, the combination with a commercialalternating current source of an electrical clock circuit adapted tohave a plurality of electric clocks connected thereto, a frequencyconverter interconnecting said commercial alternating current source andsaid electric clock circuit, means for driving said frequency converterin one direction or the other to apply substantially a given frequencyto said electric clock circuit substantially regardless of the frequencyof said commercial alternating current source, master clock means, andmeans controlled in accordance with the frequency of said electric clockcircuit and by said master clock means for regulating the operation ofthe driving means.

6. vIn a time distributing system, the combination with a commercialalternating current source of an electric clock circuit adapted to havea plurality of electric clocks connected thereto, a frequency converterinterconnecting said commercial alternating current source and saidelectric clock circuit, means for driving said frequency converter inone direction or the other to apply substantially a given frequency tosaid electric clock circuit substantially regardless of the frequency ofsaid commercial alternating current source, master clock means, anddifferential means ccntrolled in accordance with the frequency of saidelectric clock circuit and by said master clock means for regulating theoperation of the driving means in such manner as to apply a frequency tosaid electric clock circuitthat is higher than the frequency of saidcommercial alternating current source in the event that the sameis-lower than a given frequency and to apply a frequency to saidelectric clock circuit that is lower than the frequency of saidcommercial alternating current source in the event that the same ishigher than said given frequency.

'7. In a time distributing system, the combination with a commercialalternating current source of an electric clock circuit adapted to havea plurality of electric clocks connected thereto, a frequency converterhaving relatively rotatable primary and secondary winding meansconnected respectively to said commercial alternating current source andsaid electric clock circuit, driving means for rotating one of saidwinding means relative to the other in either direction, master clockmeans, and means controlled by said mast-er clock means for regulatingthe operation of said driving means to relatively rotate said windingmeans in one direction when the frequency of said clock circuit is belowa predetermined frequency and in the opposite direction when thefrequency of said clock circuit is above said predetermined frequency.

8. In a time distributing system, the combination with a commercialalternating current source of an electric clock circuit adapted to havea plurality of electric clocks connected thereto, a frequency converterhaving relatively rotatable primary and secondary winding meansconnected respectively to said commercial alternating current source andsaid electric clock circuit, driving means for rotating one of saidwinding means relative to the other, master clock means, anddifferential means controlled by said master clock means and inaccordance with the frequency of said electric clock circuit forregulating the operation of said driving means in such manner as toapply a frequency to said electric clock circuit that is higher than thefrequency of said commercial alternating current source in the eventthat the same is lower than a given frequency and to apply a frequencyto said electric clock circuit that is lower than the frequency of saidcommercial alternating current source in the event that the same ishigher than said given frequency.

9. In a time distributing system, the combination with a commercialalternating current source of an electric clock circuit adapted to havea plurality of electric clocks connected thereto, a frequency converterhaving relatively rotatable primary and secondary winding meansconnected respectively to said commercial alternating current source andsaid electric clock circuit, reversible driving means for rotating oneof said winding means in either direction relative to the other, controlmeans for said driving means disposed to effect reverse operation of thesame, master clock means, synchronous motor means connected forenergization to said electric clock circuit, and differential gearingmeans operatively interconnecting said control means with said masterclock means and said synchronous motor means.

10. In a time distributing system, the combination with a commercialalternating current source of an electric clock circuit adapted to havea plurality of electric clocks connected thereto, a frequency converterhaving relatively rotatable primary and secondary winding meansconnected respectively to said commercial alternating current source andsaid electric clock circuit, reversible driving means for rotating oneof said winding means in either direction relative to the other, controlmeans for said driving means dis# posed to effect reverse operation ofthe same, master clock means, synchronous motor means connected forenergization to said electric clock circuit, diierential gearing meansoperatively interconnecting said control means with said master clockmeans and said synchronous motor means, and lost motion means betweensaid control means and said master clock and synchronous motor means forautomatically resetting said electric clocks to the time of said masterclock means on restoration of said commercial alternating current sourceafter failure thereof for appreciable periods of time.

1l. In a time distributing system,the combination with a commercialalternating current source of an electric clock circuit adapted to havea plurality of electric clocks connected thereto, a frequency converterhaving relatively rotatable primary and secondary winding meansconnected respectively to said 'commercial alternating current sourceand said electric clock circuit, reversible driving means for rotatingone of said winding means in either direction relative to the other,control means for said driving means disposed to eiect reverse operationof the same, master clock means, synchronous motor means connected forenergization to said electric clock circuit, differential gearing meansoperatively interconnecting said control means with said master clockmeans and said synchronous motor means, and lost motion means betweensaid differential gearing means and said master clock and synchronousmotor means for permitting operation of said master clock means duringfailure of said commercial alternating current source for appreciableperiods of time and for automatically resetting said electric clocks tothe time of said master clock means on restoration of said commercialalternating current source.

FREDERICK c. HoL'rz'.

